IANAL, but closest French equivalent to Supreme Court is Conseil Constitutionnel. Cours de cassation is about breaking judgments because they were not made to the letter of the law. They do not pronounce general opinions about the law itself.

I think this is a case where the French parliamentary system doesn't map onto American institutions very well. IIRC, the Conseil Constitutionnel intervenes at the time of ratification of a law; it's a forward-looking body, unlike the US Supreme Court that judges law ex post facto (like the Cours de Cassation).